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Answer :

Answer:

D option

Step-by-step explanation:

a + b = 21

Placing value of b as 3/4a,

a + 3/4a = 21

7a/4 = 21

a = 12

Putting value of a in b=3/4a,

b = 3 × 12/4 = 9

a = 12, b = 9

Hope it helps.